Brown mite—Bryobia rubrioculus
This mite (family Tetranychidae) is a sporadic pest of almond, pear, and stone fruits, such as apricot, cherry, and plum. Note that numerous species of mites can occur on plants.
Brown mite becomes active in late winter, sooner than most other spider mites. Adults are about twice the size of most spider mites found in California. The body is oval, slightly flattened, and olive green to rusty brown. The front pair of legs are distinctly longer than the other legs.
Eggs are red and spherical and do not have a stalk arising from the top, unlike the red eggs of citrus red mite and European red mite. Larvae are bright red with three pairs of legs. After the first molt, nymphs become brown to greenish with eight legs and resemble adults.
Brown mite develops through 5 life stages: egg, 6-legged larva, 8-legged protonymph, deutonymph, and adult. Brown mites overwinter as eggs in masses on bark. Eggs are laid under bark scales and at the base of buds. Eggs hatch at the same time as leaf and flower buds open, commonly 1 to 2 weeks before the egg hatch of European red mite, which can occur on the same hosts. Brown mite egg hatch is completed before full bloom.
The mites feed on both sides of leaves. During the warmest part of the day, brown mites move off leaves and rest on shaded bark. When temperatures are cool, they move back onto leaves and feed during the night through the morning.
Adult females live 2 to 3 weeks and reproduce without mating. Males are not know to occur in this species. Brown mites are not active during hotter periods of the summer and their abundance declines in midsummer and early fall. Eggs laid during hot weather will not hatch until the following spring. About 2 to 3 generations of brown mite occur, mostly during late winter and spring.
Feeding by brown mites causes whitish gray spots on leaves. Damaged leaves become mottled, then bleached overall. Leaves fed upon by numerous mites become stunted and remain smaller than normal. This mite does not produce obvious webbing and its feeding rarely causes premature leaf drop.
Hot weather and predators cause brown mite populations to decline in summer. Western predatory mite may be brown mite's most important natural enemy. Insect predators of brown mite include brown lacewings, green lacewings, minute pirate bugs, spider mite destroyer lady beetle (ladybug), and sixspotted thrips. To improve the effectiveness of naturally occurring mite predators, control ants, minimize dust (e.g., periodically hose off small trees), and avoid the application of broad-spectrum, persistent insecticides and miticides for all pests. See Protecting Natural Enemies and Pollinators for more suggestions.
In-season sprays for brown mites are generally not warranted in residential trees to protect fruit yield or quality. If brown mite has been a problem, wait until the delayed-dormant season when buds have swollen but before they open. Then apply narrow-range or horticultural oil to thoroughly cover buds and bark.
Adapted from Integrated Pest Management for Stone Fruits, Pest Management Guidelines: Pears, and Pests of the Garden and Small Farm: A Grower's Guide to Using Less Pesticide, University of California Statewide Integrated Pest Management Program (UC IPM).
Leaf stippling from feeding of brown mite.
Adult brown mite.
Eggs and empty, hatched egg shells of brown mite.
Larva of brown mite.